1. Field of the Invention
The invention relates to optical cabling. More particularly, the invention relates to multi-fiber unit optical cabling having improved dry filling compounds.
2. Description of the Related Art
The explosive growth in demand for information-transmitting capacity in communications networks including data networks has spawned an increase in the number of optical fibers housed within optical fiber cables. Also, the increasing use of optical fibers for shorter-haul distances has further prompted a need for optical cables with larger fiber counts. Such short-haul uses include local loop applications and delivery of communication services to homes and offices. Because of these increased demands placed on optical fiber communication systems, the organization and alignment of optical fibers, e.g., for interconnection between various optical devices, has become more important to the overall performance of the optical system.
Typically, optical fiber cables include a plurality of multi-fiber units such as multi-fiber tubes. The multi-fiber tubes contain a plurality of individual optical fibers or, alternatively, a plurality of optical fiber ribbons. Conventionally, optical cabling for multi-fiber units such as multi-fiber unit tubes includes arrangements that house the multi-fiber units in a loose arrangement. See, e.g., U.S. Pat. No. 4,909,593. However, such loose arrangements have lower fiber packing densities than many conventional central core optical cables with similar fiber counts. Also, loose arrangements often must use wet filling compounds such as petroleum-based gels to reduce unnecessary shifting and/or crushing of the multi-fiber units and the individual optical fibers within the multi-fiber units. Such shifting and crushing often damages the optical fibers, e.g., by causing the individual optical fibers break or chip, thus reducing optical performance. However, many filling compounds are relatively expensive and typically are difficult to clean off or remove, thus increasing the difficulty of accessing the optical fibers within an optical cable, especially for mid-span accessing of the optical cable.
Moreover, such loose arrangements with or without conventional wet filling compounds typically do not maintain the relative position of the multi-fiber units within the cabling. Maintaining such positioning often is necessary, e.g., to preserve stranding of multi-fiber units that enhances optical performance. For example, many multi-fiber tubes include stranding patterns such as S-Z stranding to improve the bending characteristics of the optical cable by reducing strain on the optical fibers without impairing their optical performance. However, many conventional arrangements that do tend to maintain cable stranding include jackets or other suitable housing that are relatively rigid and thus pose problems accessing the optical fibers within the optical cable.
Accordingly, it would be desirable to have available optical cables that protectively encase multi-fiber units and/or fiber ribbons without the need for filling gels or other compounds. Also, the desirable optical cable should provide relatively easy access to the contents therein, but still be rigid enough to maintain any stranding arrangements of the optical fibers therein.
Embodiments of the invention include an optical communication system including an optical cable having an improved dry filling compound for protecting and maintaining multi-fiber arrangements therein and yet enabling relatively easy access thereto. The system includes a source of optical energy, an optical cable coupled to the source for transmitting optical energy from the source, and a receiver coupled to the optical cable for receiving optical energy from the source. The optical cable includes at least one multi-fiber unit tube having therein a plurality of optical fibers such as individual fibers or one or more fiber ribbons, and a dry filling compound formed around the at least one multi-fiber unit tube. The dry filling compound is made of a soft, non-adhesive plastic or rubber material and formed around the multi-fiber unit tubes in such a way that the relative position of the multi-fiber unit tubes are maintained with respect to one another within the optical cable. The dry filling compound is made of a material such as an extrudable rubber or plastic, a soft UV-curable acrylate, a soft polyolefin, a butyl rubber, or an ethylene-propylene rubber. Alternatively, the dry filling compound made from any of these materials is foamed, e.g., by chemical blowing during extrusion, gas injection during extrusion, or reactive foaming. The dry filling compound material is firm enough to maintain the relative positions of the multi-fiber unit tubes within the optical cable but soft enough to allow relatively easy access into the optical cable.